ABSTRAKT: Perhaps Plato’s most famous idea is that things like justice, piety, largeness, and equality are what he calls “forms,” which are in some significant way different from sensible things. While this is an important idea for Plato, it is hard to find an account in the dialogues of why he thinks it and how, exactly, they are supposed to be different. In this paper I argue that scholars have not understood Socrates’ account in the Phaedo because this dialogue has an unusual structure: Socrates’ account of the forms unfolds in five stages over the course of the dialogue. In order to fully understand the claims made in the first stage, one must look to the next stage, and so on until the final stage. On my account, Socrates ultimate reason for distinguishing the forms from sensible things have nothing to do with our intuitions about abstract entities nor with the distinction between universal and particular. The ultimate reason why forms cannot be sensible is because forms must do a sort of causal/explanatory work that no sensible thing could do.